Secure communications provider Silent Circle has launched a new version of its Silent Text messaging app for iPhone and iPad: Silent Text 2.

Released as a separate app rather than an update to the existing version, it’s a free download from Apple’s App Store, although a subscription to Silent Circle’s wider service – starting at $9.99 a month – is required.

“Our release of Silent Text 2.0 (ST-2) is a major rewrite of our previous product and harbinger of some of the technology that Silent Circle will be using to improve the security and refine the user experience of our customers,” explained the company on its blog.

Silent Text offers a mixture of private text chats and file transfers, with features including the ability to set how long messages can be read for; to manually delete them from the recipient’s device; and end-to-end encryption.

Among the new technologies used for Silent Text 2 are progressive encryption, to get around the fact that both participants in a conversation may not be on Silent Circle’s network at the same time.

“Ideally you should be able to start sending secure messages without waiting for the recipient to respond, but without sacrificing the same level of security and end to end encryption provided by the key exchange that we employ our current product,” explained the company.

Silent Text 2 for iPhone and iPad.

Silent Circle also says that the iOS app has been “substantially rewritten” to make it slicker to use, and also more secure:

“We walked away from Apple’s CoreData and didn’t look back. We replaced it withYapDatabase, developed by our own very talented Robbie Hanson. This gave us amazing improvements in performance and reliability as well as substantially better anti-forensics on the data at rest. All the protocol security in the world won’t help you if your device is not well protected and so we treat that with the same amount of concern.”

Silent Circle hit the headlines in 2013 when the company shut down its Silent Mail encrypted-email service “to prevent spying”. The move came after a similar service, Lavabit, was closed after rejecting a US government court order to cooperate in surveillance of its customers.